Light beam instrument



Feb. s, A1931s.

G. F. GARDNER LIGHT BEAM INSTRUMENT Wed July 24, 1956 Patented Feb. 8, 1938 v UNITED STATES PATENT OFFICE LIGHT BEAM INSTRUMENT George F. Gardner, Scotia, N. Y., assigner to GenralkElectric Com a corporation off New Application July Z4, `1936, Serial No.-9Z,433

2 Claims. (Ci. 116-114) My invention relates to electrical instruments is a schematic diagram representing a side eieand concerns particularly indicating instruments vation of the working parts 01' the apparatusof of the light-.beam type. Fig. 5. Like parts are designated by like reier- It is an object of my invention to provide a ence characters throughout in the drawing.

5 .suppressed-zero instrument having an arrange- Referring now more in detail to the drawing, ment for indicating the zero position and permitthe apparatus of Figs. 1 to 4 comprises a lightting zero adjustment of the instrument mechtight box II with a front wall I2 having a lwixulow anism. l' occupied by a translucent screen I3 marked with It is a further object of my invention to prosuitable graduations and numerals to serve as an;

lo vide a compact light-beam instrument with a indicating scale. Within the light tight box II. lo relatively great scale rangeV and high target there is a light-directing tue Il containing a clarity. source of light, such as an incandescent lamp I5,

Still another object of my invention is to profor projecting a beam oi' light I6. An instrument vide a light-beam instrument having a multiple mechanism I1 having a suitable deilecting eleset of graduations passed over successively by ment, such as a coil (not shown), carries amirl5 the indicating target. ror I8 intersecting the path of the light beam IE. Other and further objects and vadvantages will The mirror I8 is adapted to reect a beam It become apparent as the description proceeds. along the course I9 and the portion I8 of the In carrying out my invention in its preferred light beam is adapted to deflect back and forth form, I provide a light-beam instrument with a across the scale I3 in accordance with deflection w moving element capable of deecting its light of the movable element I8 caused by variations beam through-a greater angle than that subtendin the magnitude of the quantity being measured. ed by the scale or the translucent screen of the In order to increase the compactness of the instrument: For bringing the beam back on the instrument and the clarity of the graduations, scale when deilection oi the movable element is the arrangement is such that, as the measuredv such that the beam would otherwise go oif the quantity increases from zero to a predetermined end of the scale, I provide an auxiliary mirror value, the beam I9 remains on the scale 'Il and or reflector which may be stationary or may be does not approach the lower end of the scale carried by the movable element. until a predetermined value is reached, thus The invention will-be understood more readily forming a suppressed-zero instrument. This arfrom the following detailed description when rangement also permits keeping the deection considered in connection with the accompanying angle of the beam small enough to insure a clear drawing and those features of the invention .and sharply focused light spot at any position onwhich are believed to be novel and patentable the scale. In the arrangement illustrated, the

will be pointed out in the claims appended hereinstrument has a full-scale reading of twenty t0- In the drawing. Fig. 1 is a schematic dia.- and is` adapted tomeasure values between ten gram representing a plan View of the working and twenty, the values below ten being supparts of a suppressed-zero instrument constitutpressed. ing one embodiment of my invention and show- Inasmuch as indicating instruments vare sub- 40 ing the movable element in its zero position; Fig. ject to certain secular errors which cause variam 3 `is a front elevation showing the scale of the tions in the zero position and, consequently, conapparatus of Fig. 1 with a scale reading for the stant errors at every scale point, it is customary condition represented in Fig. 1; Fig. 2 is av diato provide zero-adjusting mechanism for bringgram of the'same apparatus shown in Fig. 1 with ing the indication back to zero when the measthe moving element in the position correspondured quantity is known to be zero; for examing to the lowest reading of the scale of the inple, in the case oi' an ammeter, when the meter strument; Fig. 4 is another front elevation showis disconnected. However, ln the case of suping the scale of the instrument with a scale readpressed-zero instruments, this check on the ading for the condition represented in Fig. 2;*Fig. justment is not available and, in the case oi 5 is a, schematic diagram representing aplan secular changes in the instrument or inadvertent 'view of the working parts of .another embodior unauthorized manipulation of the zero adment of my invention provided with a double tier justment, there is no way of checking the instruof scales for increasing the scale yrange of the ment except by recalibration of the scale. In instrument; Fig. 6 is a front elevation o f the aporder to overcome this diillculty, I provide an paratus of Fig. 5 showing the scale; and Fig` '1 auxiliary mirror 2n placed in the part of the 2 box where it will intercept the portion I9 of the light beam when the movable element I8 is inV the zero position. The mirror 20 is placed at such an angle thatfit reflects the beam I9 along a line 2l to strike the scale I3 at a suitable point, forexample, the minimum scale. value, ten, which is accordingly also marked zero.v If the spot of light 22 produced on the scale I3 by the light beam does not coincide with the position of the zero graduation when the instrument is disconnected from the electricalcircuit which it is measuring, its zero adjustment, not shown, is manipulated to bring the light spot 22 tothe proper position. When the measured value rises appreciably above zero, the beam Ialeaves the mirror 20 and no light spot appears on the scale I3 until the minimum value, ten of the scale is reached.

To guard against mistaking a zero indication for the reading Ill, a color illter, for example, a red filter 23. may be the light beam between the mirrors I8 and 20 or between the mirror 20 and the scale I3. A zero reading may also be distinguished from a ten reading by slightly tilting the mirror 20 so that it causes a light spot to appear above' or below the line along which the light spot would travel for readings from ten to twenty. If desired, instead of placing the auxiliary mirror 20 at a stationary position in the light box II, it may be mounted on the movable element I8 at the proper angle, as explained more in detail in connection with Fig. 5. Although the arrangement of Fig. 1 finds its principal use as a suppressedzero instrument, it will be understood that, by making the mirror 20 of suicient length or by providing a number of auxiliary mirrors corresponding to the mirror 20, the light spot 22 produced by the reflected beam 2i may be caused to traverse the scale I3 for an appreciable distance, thus extending the range of readings which may be made with the scale I3 by utilizing light spots produced both by the beam I9 reflected directly from the mirror I8 and the beam 2i reflected from the mirror 20. It will be apparent that the use of a stationary auxiliary mirror 2 9 will cause the beam 2I to deect in the opposite `direction from the beam I9, whereas mounting the auxiliary mirror on the movable element would cause the beams corresponding to the two ranges of measurement to deflect in the same direction. Y

The arrangement of Fig. 5 is intended primarily for increasing the range of deflection of a. light-beam instrument without lessening the compactness of the apparatus and clearness of the light-spot target. It will be seen that the translucent screens I3 of Figs. 2 and 3 and I3 of Fig. 6 subtend an angle oi approximately 371/2 degrees whereas deecting instruments of the moving coil and other types may readily be produced having angular deections of 90 or more degrees. Furthermore, the reilection of the beam by the moving mirror makes the angle of deection of the movable beam double the angle of deflection of the instrument element, consequently, in the ordinary single-range light-beam instrument, there is a large angle of deection of the instrument element which is unused. To make use of this unused angle of deiiection, I provide a scale or translucent screen I3 having two or more tiers or rows of graduations and I provide two or by the moi/able element ci the instrument meQhanism il at angles to each other.

interposed in the pathof.

more mirrors it and 24 carried In the speciiic arrangement illustrated, the scale I3' has an upper tier of graduations 2B for numerical values from zero to fifteen and a lower tier of graduations 26 for numerical values from fifteen to thirty. The movable mirrors Il and 24 are placed at such angles that, as the instrument I1 deects through the angle corresponding to the readings between zero and fifteen, the mirror. reilects a light beam I6' to produce a. movable beam I9' `forming a light spot 22' moving back and forth along the tier of graduations 25 of the scale I3. The mirror I8 reflects a light beam I6 to produce a movable beam I8 casting a light spot 22" moving across the lower tier 26 of the scale I3'. In the arrangement shown, the upper tier 25 carries the graduations for the lower half of the range of the instrument and the tier 26 carries the graduations for the upper half of the range of the instrument.

The invention, of course, is not limited to this specific arrangement. It will be observed that the mirrors I8 and 24 are not only at an angle to each other with respect to the axis of the moving element of the instrument I1 but are also slightly tilted so that they produce light spots 22' and 22" traveling in different parallel lines. In this Way, am' confusion is prevented as t'o whether the reading observed is within the lower or upper range of the instrument.l As a further safeguard against any such confusion, filters of different colors, for example, a red filter 21 and a green filter 28 may be provided for the movable beams I9' and I9, respectively, cooperating with the two different tiers of the scale I3'. If the color iilters are utilized for distinguishing the movable beams in the two ranges of the instrumen additional mirrors may be provided for reflecting the beams on to the same line of the scale I3' in cases where such additional compactness may be of value. If desired, the arrangement may be such that the values oi the graduations in the tiers 25 and 20 of the scale I3 overlap to a certain extent in order to check one tier against the other. For example, in the arrangement shown, the value fifteen appears on both tiers 25 and 26.

As already explained, if a greater scale range is desired, that is, a greater spacing of the graduations in each portion of the scale, this may be accomplished by providing additional movable mirrors and additional tiers in the scale Il. The arrangement is of particular value in' certain applications such as tachometer indicators for ilight testing of aircraft engines, in which a long scale is required in order to estimate true engine speed closely but which must occupy a minimum space. In some cases, no readings are required for the lower portion of the scale and the graduations from one to fifteen may be omitted, retaining only the zero graduation to facilitate adjusting the zero of the instrument as explained in connection with Figs. 1 and 3.

I have herein shown and particularly described certain embodiments of my invention and certain methods of operation embraced therein for the purpose of explaining its principle and showing its application but it will be obvious to those skilled in the arty that many modiiications and variations are possible and I aim, therefore, to cover all such modieations and variations as fall within the scope of my invention which is dened in the appended claims,

What I claim as new and desire to secure by Letters Patent of the United States is:

l., An indicating instrument oi the light-beam type comprising in combination, a source of light, a movable element carrying a pair of mirrors cooperating with said light source to cause beams of light to be reiected in response to deection of the movable element, a scale-cooperating with said light source and said mirrors so as to be traversed by said beams of light, said movable element being adapted to deect through an angle substantially greater than that required to ad- Vance one of the light beams the length of said scale and one of said mirrors being mounted at such an angle as to cause a light beam to traverse said scale during one portion of the angular movement of said movable element, the second mirror being mounted at such an angle as to cause a beam of light to traverse said scale during a succeeding portion of the angular movement of said movable element, and lters of different colors interposed in the paths of said light beams to make their appearances on said scale distinguishable for diierent portions of the movement of said movable element.

2. An indicating instrument of the light-beam type comprising in combination, a source of light, a movable element carrying a pair of mirrors cooperating with said light source to cause beams of light to be deected in response to deflection of the movable element, a scale cooperating with said light source and said mirrors so as to be traversed bygsaid beams of light, said movable element being adapted to deflect through an angle substantially greater than that required to advance one of the light beams the length of the said'scale and one of `said mirrorsbeing mounted at such an angle as to cause the light lbeam to traverse said scale during one portion of the angular movement of said movable element,

the second mirror being mounted at such an angle as to cause the beam of light to traverse said scale during a succeeding portion of angular movement of said movable element.

GEORGE F. GARDNER. 

